Resistors,compositions,pastes,and method of making and using same

ABSTRACT

PALLADIUM OXIDE OR OTHER METAL OXIDE REISTORS FOR MICROELECTRONIC CIRCUITRY ARE PROVIDED WITH A HIGH DEGREE OF REPRODUCIBILITY AND STABILITY BY FIRST CONCENTRATING TO POWDER FORM A LIQUID MIXTURE OF A RESISTOR METAL-ORGANO METALLIC COMPOUND, AT LEAST ONE OTHER STABLILIZER METAL IN ORGANOMETALLIC FORM, AND AN ANTI-AGGLOMERATING AGENT WHICH WILL NOT BURN OFF DURING PROCESSING TO FINAL RESISTOR FORM. THE POWDER IS THEN ALLOYED AND THE RESISTOR METAL OXIDIZED. THE RESULTING ALLOY IS THEN FORMED INTO A RESISTOR PASTE BY ADMIXING IT WITH A GLASS BINDER (EITHER BEFORE OR AFTER OXIDATION) AND A LIQUID CARRIER VEHICLE. THE PASTE IS PRINTED IN THE DESIRED PATTERN, DRIED AND FIRED TO PRODUCE THE RESISTOR IN FINAL FORM.

United States Patent 3,681,261 RESISTORS, COMPOSITIONS, PASTES, ANDMETHOD OF MAKING AND USING SAME Daniel W. Mason, West Peabody, Mass.,and Bernard Greenstein and John M. Woulbroun, Toledo, Ohio, assignors toOwens-Illinois, Inc. No Drawing. Filed July 27, 1970, Ser. No. 58,740Int. Cl. B44d 1/02; H01b 1/06 US. Cl. 252-514 7 Claims ABSTRACT OF THEDISCLOSURE Palladium oxide or other metal oxide resistors formicroelectronic circuitry are provided with a high degree ofreproducibility and stability by first concentrating to powder form aliquid mixture of a resistor metal-organo metallic compound, at leastone other stabilizer metal in organometallic form, and ananti-agglomerating agent which will not burn ofl? during processing tofinal resistor form. The powder is then alloyed and the resistor metaloxidized. The resulting alloy is then formed into a resistor paste byadmixing it with a glass binder (either before or after oxidation) and aliquid carrier vehicle. The paste is printed in the desired pattern,dried and fired to produce the resistor in final form. t

This invention relates to electronic resistors. More particularly, thisinvention relates to electronic resistors, compositions, pastes, andmethods of making and using same particularly within the environment ofmicroelectronic circuitry. t

The art has long known of the value of palladium oxide (PdO) for use asa resistor material, particularly in microelectronic circuitry.Generally speaking, palladium oxide is formed into a resistor byadmixing palladium with a glass binder and organic vehicle to form aprinting paste. In the case of microelectronic circuitry, the paste isthen printed onto a dielectric substrate such as aluminum oxide or thelike by the use of a screen or mask of the desired mesh and formed toprovide the desired pattern. The patterned design is then fired in airto oxidize the Pd to PdO and form the ultimate resistor lamina.

In order to increase the negative temperature coeflicient of resistivity(hereinafter referred to as TCR), to regulate ultimate resistivity, andto render the stability of the PdO system acceptable, certain metals areemployed in admixture with the palladium in the paste. Such metals,which are referred to hereinafter as stabilizers, are those which do notoxidize at the temperatures used to fire the printed paste.

Many problems attend these prior art PdO resistor systems. One majorproblem is the great sensitivity of these systems to the firing processas a whole. Slight fluctuations or variations in the firing temperature,for example, greatly changed the resistivity of the resulting product.Air flow and firing times are further variables to which the ultimatecharacteristics of the final product are extremely sensitive. Suchsensitivity, of course, renders these PdO systems extremely difficult toreproduce. Not only is reproducibility low, but for some reason, notentirely understood, stability is also very low.

The term stability is well understood in the art and is used herein inaccordance with this well know meaning. That is to say, stabilitydefines that characteristic of a resistor which enables it to maintainits resistivity within tolerable limits over extended periods of timeand use.

While the stabilizer metals used in admixture with the palladium oxidegenerally provide commercially tolerable stability to the system, theyare generally found to detri- Patented Aug. 1, 1972 mentally increasethe TCR of the systems, usually far above the i0 p.p.m./ C. levelideally desired. In some instances, especially when Ag is used,stability must be sacrificed for acceptable TCR while, on the otherhand, TCR must be sacrificed for acceptable stability. In almost allinstances, reproducibility, regardless of the metal stabilizers used, isdetrimentally low.

In order to overcome these problems, the art has sought out manysolutions. Some have sought to use various additional additives toimprove the system. Others have sought to alter the starting materialsemployed such as by employing finely divided palladium oxide in thepaste or initially employing crystalline palladium or its oxide withincritical particle sizes and surface areas. Others used combinations ofthe above solutions or turned completely from the PdO system to seekother resistive metal oxide systems which might have higher stabilityand/or reproducibility. In many instances, only a modicum of success wasactually achieved. In many other instances, the manufacture was renderedso expensive as to make it economically undesirable.

It, therefore, is apparent from the above that there exists a definiteneed in the art for a PdO or other resistive metal oxide system which ishighly reproducible, has high stability, exhibits excellent TCRs,produces high quality resistors, and is economical to manufacture.

It is a purpose of this invention to fulfill this need in the art.Generally speaking, this invention fulfills this need by providing aresistor composition and/or paste which is uniquely formed in a mannerwhich insures optimum alloying of the metals and controlled homogeneousoxidation of the Pd or other resistive metal prior to firing, to theextent that the resistivity characteristics are not detrimentallysensitive to air flow, time, and temperature variations during firing;thus to provide a highly stable, reproducible resistor for good quality.In addition, because of the optimum alloying and other factors, low TCRsare obtainable.

Basically, the resistor compositions are formulated in accordance withthis invention by:

(a) Forming an admixture of a resistive metal-organometallic compound,at least one metal stabilizer in or- .ganometallic form and ananti-agglomerating agent which will remain in the system throughoutprocessing;

(b) Heating the admixture at a sufiicient temperature and for asufiicient period of time to drive 01f the organoconstituents andconcentrate the admixture to a powder; and

(0) Heating the powder at a sufiicient temperature and for a sufficientperiod of time to alloy said metals and in some instances to oxidize theresistive metal.

The above-described resistor compositions may be employed in a widevariety of ways and environments for their resistive properties. Any ofthese ways and environments, conventional in the art, are contemplatedby this invention. As alluded to hereinabove, a preferred way in whichthese resistor compositions may be used is to formulate them intoprinting pastes and print them on appropriate substrates for use inmicroelectronic circuitry.

Such pastes are formed in accordance with this invention by admixing theresistor composition in powder form with a conventional glass binder andin some instances oxidizing the resistive metals at this point.Thereafter the oxidized mixture is added to a liquid organic vehicle.The resulting paste may then be screen printed in accordance withconventional techniques in a desired pattern, dried and fired to producethe final resistor lamina. The resistors so formed generally exhibit astability factor of less than about :l% drift during normal load life(e.g., 1000-10,- 000 hours) and a reproducibility usually on the orderof about :20% of the specified resistivity.

Generally speaking any one or a combination of the conventionalresistive metals may be used in the practice of this invention. Examplesof such metals include palladium, rhodium, iridium, ruthenium, indium,and mixtures thereof. Because of the economic advantages, ease ofprocessing, good stability, and good reproducibility, the palladiumoxide system, and thus palladium, is preferred for the purposes of thisinvention.

Any of the well known stabilizing metals may be used in the practice ofthis invention. Generally, these metals are chosen for their inertnessto oxygen at the operating conditions of this invention. Although onlyone of these metals may be employed, it is preferred to use at least twometals together in amounts which have been found to synergisticallyminimize their affect upon TCR. EX- amples of these stabilizing metalsinclude silver, gold, and platinum. Examples of preferred admixtures inparts-byweight ratio for minimization of effect on TCR include AgtAu,about 4:1-1z4; PtzAg, about 8: 1-1:8; and PtzAu, about 8:1-1z8.Particularly preferred for the purposes of this invention is the AgzAuadmixture since it is found that this admixture when alloyed with Pdwill form a single phase alloy, thus further minimizing the affect offiring on the system.

Any of the well known organo-metallic compounds of the above metals maybe used, provided that they are capable of being concentrated fromadmixture to a powder form. Such, of course, generally assumes that theorgano-metallic compounds are liquids or are solids dispersed ordissolved in conventional liquid media. In addition, the organo-metalliccompounds contemplated are those from which the organic constituents arecapable of being driven off during concentration and/or to a lesserextent, during firing.

Preferred organo-metallics for the purposes of this invention are thewell known metal resinates. Particularly preferred among the metalresinates are the conventional metal mercaptans because of the ease bywhich they may be concentrated to a substantially homogeneous powder,their availability and the like. Such mercaptans are well known and maybe obtained, for example, from Englehard Industries, under such tradedesignations as Gold #8300, a mercaptan having 28.0% by weight Au;Rhodium #8826, a mercaptan having 10.0% by weight Rh; Platinum #9450, amercaptan having 26.0% by weight Pt; Palladium #7611, a mercaptan having20.0% by weight Pd; Iridium 8057, a mercaptan having 24.0% by weight Ir;and Silver 9144, a mercaptan having 30.0% by weight Ag.

Other resinates useful include the balsam based resinates examples ofwhich, obtainable from the indicated company, include Gold A-1118 andA-1119, a balsam having 24% by weight Au and 12.0% by weight Au,respectively; Rhodium A-1120, a balsam having by weight Rh; Platinum A-l121, a balsam having 12.0% by weight Pt; Palladium A-l122, a balsamhaving 9.0% by weight Pd; Iridium A-ll23, a balsam having 6.0% by weightIr; and Ruthenium A-l124, a balsam having 4.0% by weight Ru.

Specific examples of the mercaptides of the above resistive andstabilizer metals include metallic ethyl mercaptide, n-octyl mercaptide,benzyl mercaptide, tertiary amyl mercaptide, tertiary hexadecylmercaptide and the like. Other examples include the chlorometallicmercaptide such as chlorometallic tertiary hexylmercaptide-methylsulfide, chloro-metallic (e.g. Pt) methyl mercaptide-propyl sulfide,chloro-metallic isoamylmercaptide methyl sultide and the like.

The anti-agglomerating agents useful for the purposes of this inventionare those conventional materials which are inert to the system and whichwill not burn out at alloying and/ or firing temperatures. Suchanti-agglomerating agents are usually of a fine particle size, e.g.,less than about 5 microns. Examples of these agents include: ultrafinealumina, ultrafine TiO and other ultrafine refractories. Preferred forthe purposes of this invention is ultrafine silica which is purchasableunder the trademark Cab-O-Sil L-5.

This invention also envisions the use of other additives, known in theart, to the above ingredients in order to enhance, in a known fashion,one or more of the desired characteristics of the system.

As stated, the above resistor compositions of this invention are formedby first admixing the requisite amounts of resinates together in liquidform. Homogeneity is desired and thus thorough mixing of the resinatesshould be effected. For the preferred palladium systems contemplated,the resinates are admixed in proportions so as to present about 5-95 byweight of the metal content as palladium. Preferably, the Pd content is15-75% of the total metal content and more preferably from 20-65%. Theremainder of the metal content usually consists of one or morestabilizer metals.

To this homogeneous admixture of resinates there is added, withcontinuous stirring, an anti-agglomerating agent. Generally speakingthis agent is added in an amount sufficient to prevent any substantialamount of agglomeration from taking place during the later alloyingstep. Although not limited to any particular theory, it is felt that theuse of this agent greatly aids in improving the stability andreproducibility of the system.

The exact amount of anti-agglomerating agent used will, of course, vary,depending upon the system used and the type of agent employed. Generallyspeaking, however, the agent is used in an amount of about 0.5 to about15% by weight of the metal powder formed upon concentration. When a PdOsystem is employed and the agent is finely divided silica, about 5%agent by weight of the metal powder is preferred.

After addition of the anti-agglomerating agent, the mixture is heatedwith stirring for a sufficient period of time and temperature toconcentrate the mixture to a powdery solid. Generally speaking, and whenthe resinates are mercaptide based, heating to powder is conducted atabout -200 (3., preferably at about C., for about 3-4 hours. Theresulting powder is an extremely homogeneous mixture of the metalshaving the anti-agglomerating agent dispersed therein and from whichsubstantially all of the organic constituents have been removed.

The powder so formed is heated at a temperature and for a period of timesufficient to alloy the metal. Because of the homogeneity andnon-agglomerated nature of the starting powder, alloying is homogeneousand thus optimized. The resulting powdered alloy is, therefore, anantiagglomerated homogeneous powder ready for further processing.

The temperature at which alloying is effected will depend upon whetheror not oxidation of the resistive metal is desired at this point. Inthose instances where the resistive metal is to be oxidized, the processwill take place in air and the temperature of alloying will besufliciently high to permit the oxide to form but not so high as toprevent oxidation from taking place. In a palladium system, such atemperature is about 650-750 C. Of course, alloying time will beextended to insure the requisite amount of oxidation. In those instancesWhere oxidation is not to be effected at ths point, but rather effectedin a separate step, alloying is accomplished either in an inertatmosphere and/ or at temperatures at which oxidation of the resistivemetal will not occur.

In preferred embodiments of this invention, the oxidation is effected ina separate step. Preferably, the second oxidation step is effectedeither immediately following the alloying step, or after the addition tothe alloy of the glass binder when a paste is to be formed.

In those instances where oxidation is elfected immediately afteralloying, alloying is preferably carried out at a temperature higherthan that at which any substantial amount of oxidation of the resistivemetal will occur. For the preferred Pd system such a temperature isusually above about 725 C. and usually from SOD-900 C. Since alloying istime-temperature dependent, suflicient time should be allotted to allowfor complete alloying. About 1-48 hours, depending upon the size of thebatched powder, is usually sufficient for this purpose. After alloyingis effected, the temperature is then lowered to a convenient oxidizingtemperature, and if an inert atmosphere was employed, air is pumped intothe environment to effect the oxidation step. Oxidation is alsotime-temperature dependent and thus sufiicient time is allottedpreferably for as complete oxidation of the resistive metal as possible.Generally speaking, the preferred range of oxidation temperatures forthe PdO system is from about 300 C.-725 C., and more preferably, about650-725 C. Times will vary but generally speaking, times of about 1-48hours are found to be sufficient.

In those instances, as stated above, where the alloys are to be madeinto pastes, oxidation may be effected after the alloyed powder isadmixed with the glass binder of the paste composition. Generallyspeaking, this is accomplished by ball-milling a particulate glassbinder having an average particle size less than about 5 microns withthe powdered, anti-agglomerated alloy. After these ingredients arethoroughly ball-milled and thus admixed, the mixture is subjected tooxidizing conditions (i.e., the oxidation times and temperatures setforth hereinabove) to effect oxdation of the resistive metal in thealloy. Although not limited to any particular theory, it is believedthat oxidation at this point preferably to as complete an extent as ispossible, optimizes reproducibility and stability and minimizes T CRssince the substance oxidized will be that presented to the firing stepwithout any further physical comminution or the like. Where completeoxidation is effected, reproducibility is optimized since substantiallyno oxidation can occur during firing. In this respect the term completeoxidation is being used to define that point at which substantially allof the resistive metal presented for oxidation is oxidized. Thus thisterm is being used to define that degree of oxidation at whichsubstantially no further oxidation will take place during firing. Thisis not to say that all of the resistive metal in the system is oxidized,since in many instances, alloying masks some of the alloy fromoxidation.

In a preferred embodiment wherein the Pd system is employed, oxidationafter glass binder addition is conducted between about 300 to 450 C. fora period of about 8 to 48 hours. Using such conditions, oxidation isfound to be substantially complete.

With respect to the degree of oxidation effected, resistivity can becontrolled by the amount of oxdation, and thus it is contemplated thatoxidation, regardless of how it is effected, does not necessarily haveto be complete, but rather only to a degree sufiicient to afford thedesired resistivity. This invention, however, contemplates in itspreferred form and regardless of how oxidation is accomplished, the useof oxidizing conditions such that as complete oxidation (as definedabove) as possible is obtained. This insures maximum reproducibilitywhile ultimate resistivity is controlled by the amount of resistivemetal initially employed and/ or the alloying cycle chosen.

As stated hereinabove and regardless of which oxidation procedure isemployed, the resistor compositions of this invention may be formulatedinto printing pastes, especially for use in microelectronic circuitryprinting. Such printing pastes may be formed by any conventionaltechnique. Generally speaking a preferred technique is to admix thealloyed powder with a glass binder (before or after oxidation asdescribed) and a suitable volatile organic liquid binder.

Glass binders for use in the pastes of this invention are conventionaland generally speaking, any of these conventional binders may beemployed. Examples of such binders include the boro-silicates andparticularly the lead-alumina-borosilicates. A particularly preferredglass binder, in particulate form, having an average particle size ofless than about 5 microns, is represented by (in weight percent):

The organic liquids used are conventional and generally speaking, anyone of these well-known liquids may be employed. Examples of theseliquids include butyl Carbitol acetate (diethylene glycol monobutylether acetate), iso-amyl salicylate and mixtures thereof. A particularlypreferred liquid vehicle is a mixture of 2 parts by weight butylCarbitol acetate to 1 part by weight iso-amyl salicylate.

In a preferred manner of formulating the pastes contemplated by thisinvention, the alloy and glass binder are first thoroughly admixed as byball-milling and thereafter the resulting admixture is stirred androller milled into the requisite amount of liquid vehicle to provide aprinting paste of the desired consistency. The paste so formed may thenbe printed in a desired pattern using a conventional screen or mask.Thereafter, the printed design is dried and fired to produce the finalresistor, usually upon a dielectric substrate. Drying after printing maybe effected by either air drying and/or oven drying, usually at atemperature of about -125 C. for about 5-10 minutes. Firing is usuallyaccomplished thereafter at a temperature of about 700 C. i50 C. (for thePdO- system) using a heat-up peak and cool-down cycle of about 20-60minutes with firing at peak temperatures for about 2-15 minutes.

As stated hereinabove, the resulting printed resistors of this inventionare found to be highly reproducible, have excellent stability, andgenerally have TCRs less than :500 p.p.m./ C., usually less than i200p.p.m./ C., and in some instances, substantially close to 0 p.p.m./ C.

The following examples are presented as illustrative of this invention:

EXAMPLES 1-20 Liquid admixtures were formulated from metallic mercaptanshaving the indicated metal content and Cab-O- Sil L-5 as ananti-agglomerant in an amount of 5% by weight of the total metalcontent. The liquid mixtures were then heated in open porcelaincrucibles for about 3-4 hours, i.e., until a powder formed, at atemperature of C. Sufficient liquid was formulated and heated for eachexample so that about 50 gms. of powder resulted.

The temperatures resulting were then raised in an air environment to theindicated alloying temperature and held at this temperature for theindicated period of time to insure substantially homogeneous alloyingand removal of substantially all remaining organics. In some instances(where no oxidation time and temperatures are reported) oxidation wasconducted simultaneously with alloying. In other instances, oxidationtook place after alloying in a separate step at the indicatedtemperature and for the indicated period of time. In Examples 1-11 and20 oxidation was effected before glass binder addition while in Examples12-19, oxidation was effected after addition of the glass binder andball milling hereinafter described.

Powder-glass binder mixtures were made by ball-milling for 96 hours at50-50 weight percent size less than about der with a glass frit having aparticle size less than about 5 microns and consisting of by weight: 10%SiO 25% B 0 5% A1 0 25 ZnO; and 35% PhD. The ball-mill employed was asize 00 mill and milling was done with an aluminum oxide based mill andacetone. The resulting powders were then dried of acetone (and inExamples 12- 19 where then oxidized) and pastes were made.

The pastes were formulated by using 3 parts by weight powder and 1 partby weight organic liquid vehicle. The organic liquid vehicle consistedof 15% by weight T-10 ethyl cellulose dissolved in 85% by weight of 2parts by said anti-agglomerating agent being selected from ultrafinesilica and an ultrafine refractory. 2. A resistor composition accordingto claim 1 wherein said resistive metal is palladium.

weight butyl Carbitol acetate and 1 part by weight iso- 3. A resistorcomposition according to claim 1 whereamyl salicylate. in saidorganometallc compounds are mercaptans.

The pastes were then printed upon 1 inch square alu- 4. A resistorcomposition according to claim 1 which minum oxide substrates using a200 mesh stencil screen. includes two metal stabilizers having a metalcontent The printed design was then air dried at about 100 C. weightratio selected from AgzAu, about 4:1-124; PtrAg, for about 5 minutes andthen fired in an open air conabout 8:1-1z8; and PtzAu, about 8:1-1z8.tinuous belt conveyor kiln, except in Examples -17 5. A resistorcomposition according to claim 4 wherein where a box kiln was used,using the indicated firing cycle. said resistive metal is palladium.

The results, reported in the following table were obtained: 6. Aresistor composition according to claim 1 wherein TABLE A Firing TotalAlloying Alloying oxidizing oxidizing Firing time firing Metal wt.percent, temp. time temp. time temp., (min. at time Resistance TOR,

Example organo metallic 0.) (hrs) 0.) (hrs.) 0. (peak) at peak) (min.) Kohms/sq. p.p.m./C.

1 Pd, 65; Ag, 28; Au, 7 800 16 725 72 700 6.0 24.0 11.0 +40 2 Pd, 65;Ag, 28; Au, 7 725 16 700 6.0 24.0 5.0 +145 3 Pd, 40; Ag,48; Au, 12-.-;725 16 700 6.0 24.0 6.2 +396 4 Pd, 40; Ag, 48; Au, 12... 800 16 725 16700 6.0 24.0 1.8 +415 5 Pd, 60; Ag, 32; Au, 8 850 8 725 8 700 6.0 24.04. 0 +325 6 Pd, 50; Ag, 40; Au, 10 725 16 700 6.0 24.0 17 +100 12 Pd,35; Ag, 52; Au, 13.-." 800 16 400 16 710 8 40 1.17 10 13 Pd, Ag, 52; Au,13.--" 400 16 710 s 0125 A25 14 Pd, 35; Ag, 52; An, 13 a 725 8 400 710 840 4. 9 +315 15 Pa, 35; Ag, 52;Au,13 800 16 400 16 700 10 30 1.3 0

16 Pd, 35; Ag, 52; An, 13"... 400 16 700 10 30 180 0 17 Pd, 35; Ag, 52;Au, 13--. 3 725 8 400 16 700 10 30 50 600 18 Pdf 50; A 40; Au, 10 331;1g 400 16 710 6 30 .800 +439 19 Pd, 50; Ag, 40; Au, 10 1 12 13 400 40710 6 30 1.5 +450 20 Pd, 35; Pt, 8; Ag,57 800 16 700 6 24 .0073 +169 148% glass binder used. 2 48.6% glass binder used.

Once given the above disclosure, many other features, modifications andimprovements will become apparent to the skilled artisan. Such otherfeatures, modifications and improvements are, therefore, considered tobe a part of this invention, the scope of which is to be determined bythe following claims.

We claim:

1. A resistor composition comprising a resistive metalorganometalliccompound, at least one metal stabilizer in organometallic form and ananti-agglomerating agent which is inert to the system and which preventsagglomeration of the resistive metal and metal stabilizer duringalloying thereof, which alloying is conducted prior to the firing of thecomposition into a resistor structure,

said resistive metal being selected from the group consisting ofpalladium, rhodium, iridium, ruthenium, indium, and mixtures thereof;

said metal stabilizer being selected from the group consisting ofsilver, gold, and platinum and mixtures thereof; and

a In run 3 insufficient alloying (too low temp. and time) was effectedto achieve good reproducibility.

the metal content of the composition is 5-95% by weight resistive metal.

7. A resistor composition according to claim 1 wherein said resistivemetal is palladium and the metal content of said composition is l5-75%by weight palladium, the remainder of the metal content consistingessentially of said stabilizer metal.

References Cited

